experimental affine2d loading

[skjerns]

Trying to add experimental support for affine2d, it seems Claude Code figured out how to read it

 HDF5 Structure Discovery

  MATLAB stores affine2d objects using the same MCOS encoding as datetime:
  - Each variable is a (1,6) uint32 dataset with MATLAB_object_decode=3
  - Field [4] + 1 gives the index into #subsystem#/MCOS
  - Each MCOS entry is a Group containing TransformationMatrix (3×3 float64)
  - The matrix is stored transposed → apply .T to recover MATLAB's .T property

closes #43

[gemini-code-assist]

Summary of Changes

Hello @skjerns, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the mat73 library's capability by introducing experimental support for MATLAB's affine2d objects. This allows users to correctly load and interpret 2D geometric transformation data stored in .mat files, expanding the range of MATLAB data types that can be seamlessly integrated into Python workflows. The implementation focuses on accurately extracting the transformation matrices and includes robust error handling and comprehensive testing to ensure reliability.

Highlights

• Experimental affine2d support: Added experimental support for loading MATLAB affine2d objects from HDF5-based .mat files (v7.3 and later). This involves parsing the MCOS encoding used by MATLAB for these objects.
• Robust parsing logic: Implemented detailed logic to extract the TransformationMatrix from affine2d objects, including checks for expected HDF5 structure, MCOS references, and data integrity, with verbose error logging for unsupported formats.
• Comprehensive test coverage: Introduced a new MATLAB script (create_mat.m) to generate a test .mat file containing various affine2d transformations (identity, translation, scaling, rotation, shear, combined, and within structs/cell arrays). A corresponding Python test case (test_affine2d_loading) was added to verify the correct loading and transformation matrix values for all these scenarios.

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Changelog

• mat73/core.py
  • Added a new elif block within the convert_mat method to handle mtype=='affine2d'.
  • Implemented logic to navigate the HDF5 structure, specifically the #subsystem#/MCOS group, to locate the TransformationMatrix for affine2d objects.
  • Included validation checks for MATLAB_object_decode attribute, MCOS subsystem presence, data shape, and MCOS index range.
  • Ensured the TransformationMatrix is correctly transposed to match MATLAB's property.
• tests/create_mat.m
  • Appended MATLAB code to create a new .mat file named testfile_affine2d.mat.
  • Defined various affine2d objects representing identity, translation, scaling, rotation, combined transformations, and shear.
  • Included affine2d objects within a struct and a cell array to test complex data structures.
  • Saved all created affine2d variables into testfile_affine2d.mat using the -v7.3 format.
• tests/test_mat73.py
  • Updated the setUp method to include the path to the new testfile_affine2d.mat.
  • Added a new test method test_affine2d_loading to verify the correct parsing of affine2d objects.
  • Implemented assert_allclose checks using numpy to compare loaded transformation matrices against expected values for all affine2d types created in create_mat.m.

Activity

• The author, skjerns, created this pull request to add experimental support for affine2d loading, referencing issue ERROR:root:ERROR: MATLAB type not supported: affine2d, (uint32) #43.
• The pull request description includes details on the HDF5 structure of affine2d objects, as discovered by Claude Code.

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[gemini-code-assist]

Code Review

This pull request introduces experimental support for loading MATLAB affine2d objects from HDF5 files. The implementation in mat73/core.py includes robust checks for the HDF5 structure and data integrity related to affine2d objects. Comprehensive test cases have been added in tests/create_mat.m and tests/test_mat73.py to cover various affine2d transformations and their embedding within MATLAB structs and cell arrays. The changes appear correct and well-tested, enhancing the library's capability to handle more complex MATLAB data types.